Phylogeny of the Pteraspidiformes (Heterostraci), Silurian–Devonian jawless vertebrates

Abstract

The Pteraspidiformes are an order of armoured agnathans of Silurian and Devonian age composed of five families: the Anchipteraspididae, Protopteraspididae, Pteraspididae, Protaspididae and Psammosteidae. Relationships within the order are poorly known and although past attempts have been made to represent the state of knowledge in this area none have attempted a rigorous computer-based analysis. Here we present the results of the cladistic analysis on a matrix comprising 25(+1) taxa and 59 characters using W INCLADA . The first analysis was run without any representative of the Psammosteidae and supports the presence of five groups within the order although one, the 'Protopteraspididae', is paraphyletic and a second, the Gigantaspididae, is newly recognized. In a second analysis the addition of the psammosteid Drepanaspis gemuendenensis results in a better resolved tree in which the basal family, the Anchipteraspididae, are clearly monophyletic and in which the Psammosteidae, as represented by Drepanaspis , is the next less inclusive. This is contrary to the previous view that the psammosteids were an advanced clade within the Pteraspidiformes.

Phylogenetic relationships of psammosteid heterostracans (Pteraspidiformes), Devonian jawless vertebrates

“…Protopteraspis vogti fall in the one clade with the derived pteraspids and psammosteids. In Pernegre and Elliott's (2008) phylogeny, Doryaspis was within the 'Protopteraspididae' , but here Doryaspis and Woodfjordaspis fall within the same clade of Pteraspidoidei (family Doryaspididae N. Heintz in Tarlo 1962), and Xylaspis is included in the Protaspididae. Psammosteids contain six families: Drepanaspididae, Guerichosteidae, Obrucheviidae, Pycnosteidae, Psammolepididae and Psammosteidae.…”

“…falcatus. For testing various hypotheses of derivation of the psammosteids (Janvier, 1996;Pernègre, 2002;Pernègre and Elliott, 2008;Randle and Sansom 2016), eight taxa of the order Pteraspidiformes, which may form the sister group to psammosteids, were encoded: Anchipteraspis crenulata, Doryaspis nathorsti, Errivaspis waynensis, Gigantaspis laticephala, Protaspis bucheri, Protopteraspis vogti, Woodfjordaspis felixi, and Xylaspis prima. Two cyathaspidiform taxa, Anglaspis PALAEONTOLOGY maccoulloughi (outgroup taxon in TNT) and Nahanniaspis mackenziei were chosen as outgroups, because they are very useful in polarizing character states within the analysis (Pernègre and Elliott, 2008;Randle and Sansom, 2016).…”

“…Characters used in the phylogenetic analysis were obtained from direct study, published descriptions, or were taken unchanged or adapted from previous phylogenies (Ilyes and Elliott 1994;Pernègre, 2002;Pernègre and Goujet, 2007;Pernègre and Elliott, 2008;Randle and Sansom, 2016) (Appendix 1). Figure 2 provides a visual explanation of some ratios of plates, which were used in character codings.…”

“…The close relationship between Doryaspis and psammosteids was criticized (Elliott and Mark-Kurik, 2005, p. 107) due to differences in squamation and position, pattern and number of plates in their cephalothoraxes. Pernègre and Elliott (2008) published a strict consensus tree including Drepanaspis gemuendenensis, based on a substantially improved and expanded matrix. According to their cladogram, psammosteids are also included in the order Pteraspidiformes and placed between the basal family Anchipteraspididae and the family 'Protopteraspididae' (Pernègre and Elliott, 2008, Fig.…”

“…Currently psammosteids are often regarded as the family Psammosteidae (Janvier 1996;Pernègre and Elliott, 2008;Randle and Sansom, 2016). Also they are assigned to the suborder Psammosteida in the order Pteraspidiformes (Elliott, Mark-Kurik, and Daeschler, 2004;Glinskiy and Mark-Kurik, 2016;Glinskiy and Nilov, 2017).…”